1. Field of the Invention
The present invention relates to chiral porous metal phosphonates synthesized via a molecular building block approach. The chiral porous metal phosphonates may function as catalysts for enantioselective heterogeneous asymmetric reactions such as asymmetric hydrogenation of a variety of prochiral substrates including alpha- and beta-keto esters, diketones, hydroxy ketones, simple ketones, enamides, and acrylic acid derivatives.
2. Description of Related Art
Asymmetric reduction of prochiral olefins, ketones and imines is a powerful method for the production of optically active compounds. For example, catalytic asymmetric hydrogenation is one of the most efficient strategies for the synthesis of optically active molecules. In particular, ruthenium and rhodium complexes of chiral chelating bisphosphines such as the Ru and Rh complexes of 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) have been used for the reduction of a wide range of substrates including keto esters, alkenes, and ketones with high enantioselectivity. See, for example, Angew. Chem., Int. Ed. 2002, 41, 2008; J. Am. Chem. Soc. 2002, 124, 4952; Acc. Chem. Res. 1990, 23, 345. J. Am. Chem. Soc. 1988, 110, 629; EP 1 254 885. J. Am. Chem. Soc. 1995, 117, 10417; Angew. Chem. Int. Ed. 1998, 37, 1703; J. Am. Chem. Soc. 2000, 122, 6510; J. Am. Chem. Soc. 1998, 120, 13529; J. Am. Chem. Soc. 2002, 124, 6508. However, these complexes suffer from a number of disadvantages such as the high costs of both noble metals and chiral ligands and the necessity and difficulty in removing trace amounts of metals from the organic products. These disadvantages have hindered the application of homogeneous catalysts in many industrial processes.
Various methods of providing improved catalysts have been attempted. One of these methods is the heterogenization of homogeneous asymmetric catalysts as described in Chem. Rev. 2002, 102, 3385. Heterogenized catalysts may combine advantages of homogeneous and heterogeneous systems and provide solutions to both recycling and reusing expensive catalysts and preventing the leaching of metals. To date, several approaches have been used to heterogenize homogeneous asymmetric catalysts including attachment to porous inorganic oxide and insoluble organic polymer supports, incorporation into soluble organic macromolecules and membranes, and immobilization via biphasic systems.
For application in industrial asymmetric catalysis, however, an asymmetric hydrogenation or other catalyst needs to exhibit high activity and enantioselectivity in the desired transformation of a particular substrate. It is also important that the chiral ligand precursor can be prepared efficiently by a synthetic route that is amendable to scale-up. The heterogenized catalysts afforded by the previous methods, however, do not meet these requirements and are typically less effective than their homogeneous counterparts.
Thus, there is still a need in the art for effective heterogeneous asymmetric catalysts, methods of making such catalysts and methods of using heterogeneous asymmetric catalysts for a variety of asymmetric reactions. The present invention provides such heterogeneous asymmetric catalysts and methods.